swift - CIImage内存未释放

Question

我正在尝试拍摄一系列图像，同时混合 X 图像并生成新图像。这是我必须完成的代码:

static func blendImages(blendFrames: Int, blendMode: CIImage.BlendMode, imagePaths: [URL], completion: @escaping (_ progress: Double) -> Void) {
    var currentIndex = 0

    while currentIndex + blendFrames < imagePaths.count {            
        let currentSubset = Array(imagePaths[currentIndex..<(currentIndex + blendFrames)])

        var currentSubsetIndex = 0

        var firstImage: CIImage?

        while currentSubset.count > currentSubsetIndex + 1 {                
            if firstImage == nil { firstImage = CIImage(contentsOf: currentSubset[currentSubsetIndex]) } //First image allocated in memory

            if let secondImage = CIImage(contentsOf: currentSubset[currentSubsetIndex + 1]) {//Second image allocated in memory
                firstImage = firstImage?.blend(with: secondImage, blendMode: blendMode)
            } //Would expect secondImage to be freed from memory at this point, but it does not happen

            currentSubsetIndex += 1
        } 

        if let finalImage = firstImage {
            let bitMapRep = NSBitmapImageRep(ciImage: finalImage)
            let data = bitMapRep.representation(using: .jpeg, properties: [:])

            do {
                try data?.write(to: URL(fileURLWithPath: "Final-" + String(format: "%03d", currentIndex) + ".jpg"))
            } catch let error as NSError {
                print("Failed to write to disk: \(error)")
            }

        }

        firstImage = nil //Would expect firstImage to be freed from memory at this point (or at beginning of next cycle in while-loop), but it does not happen

        currentIndex += 1
    }
}

以及 CIImage 的 blend 函数的代码

extension CIImage {

    enum BlendMode: String {
        case Lighten = "CILightenBlendMode"
        case Darken = "CIDarkenBlendMode"
    }

    func blend(with image: CIImage, blendMode: BlendMode) -> CIImage? {
        let filter = CIFilter(name: blendMode.rawValue)!
        filter.setDefaults()

        filter.setValue(self, forKey: "inputImage")
        filter.setValue(image, forKey: "inputBackgroundImage")

        return filter.outputImage
    }
}

如代码注释中所述，我希望在 firstImage 和 secondImage 中分配的内存在创建它们的范围结束时被释放。因为它们都是在 while 循环中创建的，所以我希望它们在该循环结束时被释放，然而，这似乎没有发生。但是这里没有内存泄漏，因为当 blendImages 函数完成时，内存被适本地释放(但是，这为时已晚，因为代码可能会运行数百或数千张图像，从而使应用程序消耗几个 TB 的数据，然后才被释放)。如果有人能看到我的代码中的缺陷以及如何提高内存效率，我们将不胜感激。

Answer 1

你应该使用 autoreleasepool函数强制释放其范围内的对象。此功能将帮助您更精确地管理内存占用。

static func blendImages(blendFrames: Int, blendMode: CIImage.BlendMode, imagePaths: [URL], completion: @escaping (_ progress: Double) -> Void) {
    var currentIndex = 0

    while currentIndex + blendFrames < imagePaths.count {
        autorelease {
            // your code
        }

        currentIndex += 1
    }
}

你可以查看这个post获取更多信息。